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Postfix: The Definitive Guide by Kyle D. Dent

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Chapter 3. Postfix Architecture

You can easily manage and operate Postfix without understanding everything about how it works. If you're ready to dive right in, you can skip this section and start at the beginning of the next chapter. It might be difficult to digest all of the material here if you don't have much experience with Postfix yet, but this chapter will give you an overview of the various pieces, which might come in handy as you start to work with Postfix. Later, after you have more experience with Postfix, you might want to return to this chapter to try to absorb more of the details.

Postfix Components

The architecture of Postfix is quite different from that of a monolithic system such as Sendmail, which traditionally uses a single large program for its handling of email messages. Postfix breaks down tasks into separate functions using individual programs that each perform one specific task. Most of these programs are daemons, which are processes that run in the background on your system. The master daemon is started first, and it invokes most other processes, as needed. Postfix daemons that are invoked by the master daemon process their assigned tasks and terminate. They might also terminate after a configured amount of time or after handling a maximum number of requests. The master daemon is resident at all times, and gets its configuration information at startup from both main.cf and master.cf. See Chapter 4 for more information on Postfix configuration files.

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